In recent years, reduction of emissions of carbon dioxide is strongly desired in order to cope with air pollution and global warming. In the automobile industry, the reduction of emissions of carbon dioxide is highly expected in association with the spread of electric vehicles (EV) and hybrid electric vehicles (HEV). Therefore, development of secondary batteries for driving motors as a key to practical application of such vehicles, is actively being carried out.
As for the secondary batteries for driving motors, lithium ion secondary batteries having high theoretical energy are gaining increasing attention and are therefore being developed rapidly. In general, a lithium ion secondary battery has a configuration in which several sets of a positive electrode, a negative electrode and an electrolyte layer interposed between these electrodes, are housed in a battery case. The positive electrode is obtained in a manner such that positive electrode slurry containing a positive electrode active material is applied to a surface of a current collector. The negative electrode is obtained in a manner such that negative electrode slurry containing a negative electrode active material is applied to a surface of a negative electrode current collector.
In order to improve capacity characteristics and output performance of the lithium ion secondary battery, it is quite important to determine the respective active materials of the lithium ion secondary battery.
There is known a battery using a positive electrode active material containing a lithium composite oxide represented by chemical formula: Li1+a[MnbCocNi(1-b-c)](1-a)O(2-d), as proposed in Japanese Patent Unexamined Publication No. 2007-220630. In the chemical formula, a, b, c and d respectively satisfy the conditions: 0<a<0.25, 0.5≦b<0.7, 0≦c<(1−b) and −0.1≦d≦0.2.